The present invention relates to a method of measuring the dimensions of an object in several directions, with a light beam being deflected over the object in the direction to be measured and a conclusion being drawn from the duration of the interruption of the light beam by the object as to the dimensions of the latter. Methods and apparatuses of this type are known in which the optical system is configured in such a way that a telecentric light beam at a known velocity or, more precisely, with a known velocity curve, is deflected through the measuring field so that the duration and position of the interruption of the light beam permit a precise conclusion as to the dimensions and possibly the position of the object.
In order to detect the dimensions of an object in several directions, generally in two directions (x, y) that are disposed at a right angle to one another, the light beam deflected by a deflection member, for example a rotating or oscillating mirror, is conducted through an objective lens which produces a telecentric light beam and to a beam divider from which two light beams travel simultaneously over suitable mirror systems into the measuring field where they are deflected in synchronism in two mutually perpendicular directions. Although this arrangement requires only one light source and one objective lens, it is connected with considerable drawbacks. The division of the light beam into two light beams and their introduction into the measuring field by way of mirror systems does not permit the measuring device to have a compact structure. It is difficult and expensive to configure and set the optical system so that the two light beams created from one light beam that passes through a common objective lens are focused in an optimum manner. A very precise measurement of even the smallest dimensions, however, requires very precise focusing of the light beams at the location of the object. The common objective lens disposed upstream of the beam divider and the mirror systems is relatively far removed from the object and also from windows in the housing of the measuring instrument through which the light beams enter the measuring field. When passing through the windows, the light beams focused onto the object already have a relatively small cross section so that impurities possibly present on these windows could, under certain circumstances, have a considerable, interfering influence on the light beams. As mentioned, the two light beams pass through the measuring field in synchronism, that is, the measurement signals corresponding to this passage of light occur practically in synchronism and must be processed in separate measuring channels.